# frozen_string_literal: true

require 'schnorr'
require 'json'

module Nostr
  # Each user has a keypair. Signatures, public key, and encodings are done according to the
  # Schnorr signatures standard for the curve secp256k1.
  class User
    # A pair of private and public keys
    #
    # @api public
    #
    # @example
    #   user.keypair # #<Nostr::KeyPair:0x0000000107bd3550
    #    @private_key="893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900",
    #    @public_key="2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558">
    #
    # @return [KeyPair]
    #
    attr_reader :keypair

    # Instantiates a user
    #
    # @api public
    #
    # @example Creating a user with no keypair
    #   user = Nostr::User.new
    #
    # @example Creating a user with a keypair
    #   user = Nostr::User.new(keypair: keypair)
    #
    # @param keypair [Keypair] A pair of private and public keys
    # @param keygen [Keygen] A private key and public key generator
    #
    def initialize(keypair: nil, keygen: Keygen.new)
      @keypair = keypair || keygen.generate_key_pair
    end

    # Builds an Event
    #
    # @api public
    #
    # @example Creating a note event
    #   event = user.create_event(
    #     kind: Nostr::EventKind::TEXT_NOTE,
    #     content: 'Your feedback is appreciated, now pay $8'
    #   )
    #
    # @param event_attributes [Hash]
    # @option event_attributes [String] :pubkey 32-bytes hex-encoded public key of the event creator.
    # @option event_attributes [Integer] :created_at Date of the creation of the vent. A UNIX timestamp, in seconds.
    # @option event_attributes [Integer] :kind The kind of the event. An integer from 0 to 3.
    # @option event_attributes [Array<Array>] :tags  An array of tags. Each tag is an array of strings.
    # @option event_attributes [String] :content Arbitrary string.
    #
    # @return [Event]
    #
    def create_event(event_attributes)
      event_fragment = EventFragment.new(**event_attributes.merge(pubkey: keypair.public_key))
      event_sha256 = Digest::SHA256.hexdigest(JSON.dump(event_fragment.serialize))

      signature = sign(event_sha256)

      Event.new(
        id: event_sha256,
        pubkey: event_fragment.pubkey,
        created_at: event_fragment.created_at,
        kind: event_fragment.kind,
        tags: event_fragment.tags,
        content: event_fragment.content,
        sig: signature
      )
    end

    private

    # Signs an event with the user's private key
    #
    # @api private
    #
    # @param event_sha256 [String] The SHA256 hash of the event.
    #
    # @return [String] The signature of the event.
    #
    def sign(event_sha256)
      hex_private_key = Array(keypair.private_key).pack('H*')
      hex_message = Array(event_sha256).pack('H*')
      Schnorr.sign(hex_message, hex_private_key).encode.unpack1('H*')
    end
  end
end